1. Field of the Invention
Embodiments of the present invention generally relate to computer programming techniques for graphics processing systems. More specifically, embodiments of the invention relate to parameter buffer objects used to store shader program parameters.
2. Description of the Related Art
Over the past decade, the cost of adding on-chip logic to processors has substantially decreased. Consequently, certain types of processors, such as advanced graphics processing units (GPUs), now include functionality not previously available in earlier GPU designs. For example, a GPU may include multiple texture image units used to store references to texture maps used in graphics rendering operations. One benefit of this new capability is that more efficient texture mapping operations and the like may now be performed on the GPU, thereby increasing overall performance in the graphics pipeline.
To fully realize the additional processing capabilities of advanced GPUs, as much GPU functionality as possible needs to be exposed to graphics application developers. Among other things, doing so enables graphics application developers to tailor their shader programs to optimize the way GPUs process graphics scenes and images. Exposing new GPU processing capabilities to graphics application developers requires that the application programming interface (API) be configured with new calls and libraries that make new features and functionalities directly accessible by developers.
Programmable shader programs executing on a GPU repeatedly perform operations accessing attributes of individual inputs (vertices or fragments) and may also access a set of values that are constant over a set of inputs. Such constants are often referred to as “uniforms” or “program parameters.” For example, a vertex shader may perform lighting calculations where the position, direction, and intensity of each light source are stored as uniforms and read by the vertex shader. The use of uniforms in a programmable shader allow an application to access a relatively large amount of data describing a given scene without transmitting all the data for each vertex or fragment processed.
When rendering an image, an application may use a variety of shader programs, each performing a different operation. Although each shader program may be configured to perform a specific function, two or more shader programs may rely upon the same constant data. For example, two or more shader programs may perform lighting operations that use the same data (e.g., lighting information). However, current graphics APIs provide very limited ability to share uniforms among multiple shader programs, and may even require that the same uniform data be duplicated for each shader program. Additionally, a single shader program may operate using different sets of uniforms. For example, different portions of a scene may be illuminated by different lights. Using current APIs, combining all uniforms used over the scene into one large collection may run into implementation-dependent limits on the amount of uniform storage. Dynamic updates to a small set of uniform values can reduce uniform storage requirements, but can incur substantial CPU and GPU overhead. Additionally, updates may require a pause in the highly pipelined GPU to wait for threads using the old values of the uniforms to complete before the update can be performed.
Since the computational power of the GPU relative to the CPU has increased dramatically over the years, applications have progressively moved more computation onto the GPU. For example, applications may perform physics simulations (e.g., computing the position of a set of particles) on the GPU, by executing a shader program on one or more of the processing units of the GPU. The results of those simulations may be used in a variety of ways, including as uniform values for subsequent computations. To perform the next sequential processing pass, however, it is often necessary to transmit the results back to the CPU and through the API so that the data can be sent to the appropriate processing unit of the GPU. This process of moving uniform datasets between the CPU and the GPU can result in a substantial performance penalty.
As the foregoing illustrates, what is needed in the art is a mechanism that provides greater efficiency and flexibility for using bindable uniforms and parameter buffer objects relative to current techniques.